The present invention relates to a weft brake, particularly for weaving looms and the like.
As it is known, weft thread is fed to weaving looms by unwinding the weft thread from a spool which is arranged ahead of a weft thread feeder, from which the thread is then sent to the weaving loom or other textile machine.
Electrically-actuated weft brakes are typically inserted between the spool and the feeder and between the feeder and the loom and are meant to modulate the mechanical tension of the thread in order to adapt it to the weaving requirements.
Modulation of the braking action is achieved in several conventional manners and in particular by passing the thread between two laminar elements, respectively a fixed one and a movable one, and by varying the mechanical pressure with which the movable element is pressed against the cooperating fixed element.
As an alternative, both the fixed element and the movable element are comb-shaped, with tines ending with transverse bars which mutually interpenetrate, varying the degree of mutual penetration of the two combs, which accordingly deflect to a greater or smaller extent the path of the thread, correspondingly braking its sliding.
In both cases, the movable element of the weft brake is moved by an electric actuator which is supplied with a current modulated according to the modulation of the intended braking action.
As it is also known, the movable element of weft brakes is actuated by means of linear electric motors, particularly with three-pole motors having very high intervention speeds and requiring very low excitation currents.
Conventional weft brakes of the specified type, while providing excellent performance in terms of braking action, suffer drawbacks and in particular are not entirely satisfactory as regards the possibility to modulate the braking action.
Moreover, the weft brakes can break the thread rather easily, especially in the presence of uneven portions, e.g. in the presence of knots or weaker portions of the thread.